tapping stainless

[nekshot]

I have a project that is requiring I tap the scope rings. I bought these off ebay as stainless steel but I don't know if that is the metal or the finish. How would you go about tapping these? I only need one tap in bottom of ring stem so I can fasten them to a dove tail.

[Rick Hodges]

Tap just like any other steel...go slow lots of lube, back out and clear chips often. Drilling pilot hole, slow rpm and heavy feed. Oh yeah, high speed or cobalt taps, not carbon.

I spent 6 years as a machinist making jet engine parts out of all sorts of stainless steels, inconels, monels and titanium. Most 400 series stainless steels (magnetic) are no more difficult to machine that carbon steel. The higher grades (316, 321) are not hard but are tougher. Slower speed and higher feed rates than carbon steel.

[country gent]

Stainless is a generic term like carbon steel aluminum. Unless you know the grade of stainless it a pretty broad range. Stainless Steels are tougher and a little more "stringy in some grades making getting chips to break a little trickier. Use a good cutting oil ( an actual cutting oil not motor oil or gun oil). If possible drill and tap in a solid mill. Drill hole to depth and at size. Lightly chamfer hole. chuck with part still in the mill put machine in nuteral and turn drill chick by hand when tapping. This keeps the tap from flexing or bending. Keep light pressure on the spindle turnng andworking chuck back and forth to break chips and clearing chips repeatedly. If its a blind hole fill with a thicker cutting fluid as this helps push chips up and out of hole. On thru holes we used alot of gun taps as these fedd the chips down thru the hole and out. Blind holes start with a starting tap if possible or a plug tap then finish with bottom tap. ( On some firearms holes the point may even needto be removed to get a good start for the bottom tap. Work slow and carefully. If possibly use a piece of scrap stainless to test and see how it goes, its much easier to break a tap in scrap than in the part.

[nekshot]

Thanks, I will have to get other taps as all I have are carbon. I will leave it in the mill and I do have cutting and tapping oils. Hopefully this whole deal comes together as it is for a tube site for my Gibbs lookalike mzl project.

[KCSO]

Tap eze or Do Drill seem to work best on stainless.

[fecmech]

I am not a machinist at all but I did D&T two Ruger stainless pistols for Weigand scope mounts with carbon taps (new ones) and Tap Magic. I practiced on a piece of stainless pipe which was considerably tougher than the Rugers and had no problems at all. Just go slow and you should be ok.

[nekshot]

yup, it was stainless and that Do-Drill really worked best. Thanks every one.

[retread]

Stainless is a generic term like carbon steel aluminum. Unless you know the grade of stainless it a pretty broad range. Stainless Steels are tougher and a little more "stringy in some grades making getting chips to break a little trickier. Use a good cutting oil ( an actual cutting oil not motor oil or gun oil). If possible drill and tap in a solid mill. Drill hole to depth and at size. Lightly chamfer hole. chuck with part still in the mill put machine in nuteral and turn drill chick by hand when tapping. This keeps the tap from flexing or bending. Keep light pressure on the spindle turnng andworking chuck back and forth to break chips and clearing chips repeatedly. If its a blind hole fill with a thicker cutting fluid as this helps push chips up and out of hole. On thru holes we used alot of gun taps as these fedd the chips down thru the hole and out. Blind holes start with a starting tap if possible or a plug tap then finish with bottom tap. ( On some firearms holes the point may even needto be removed to get a good start for the bottom tap. Work slow and carefully. If possibly use a piece of scrap stainless to test and see how it goes, its much easier to break a tap in scrap than in the part.

Good advice. Heed it and you will not be sorry.

[country gent]

The old tap magic ( what old timers called pepermint water due to smell and consistency) did work good in tool steels and stainless. It ate aluminum pretty bad. I have also seen it darken or discolor stainless steels and some machine parts when used on stainless. At work we did alot of stainless in diffrent grades ( Food industry. Campbells Soups Co.) some was pretty decent some grades tough and some were terrible for work hardening when machining. Stainless can be machined and worked with out alot of issues at slower speeds feeds and sharp tooling. I would imagine from the looks of most firearms and parts that the stainless is a free machining grade as they machine pretty decently normally.

[MtGun44]

Critical issue - use a new drill bit and push hard so that it cuts, but does NOT
spin. Even a couple rotations spinning while not cutting will harden some alloys
of stainless so you will not be able to drill them. Other alloys are more like
carbon steel in drilling. Tap magic or other good lube is critical for tapping.

[fast ronnie]

Buttercut works really well if you can find it. On another thread someone said it is being made by Aerovoe now.

[coleman]

Spend a few more $ and get a good made in USA tap and good tapping fluid

[smokeywolf]

When I tap stainless (usually type 316), as long as the threaded depth is at least equal to or greater than the thread O.D. I use a tap drill that produces no more than a 65% thread. If the intended threaded depth is double or greater than the thread O.D. you can go with a tap drill that produces as little as a 55% thread.

[JSnover]

I've 'cheated' the same way, drilling a slightly oversized hole when the job allows less engagement. You can tap stainless with carbon steel, just make sure to use a good sharp one and go easy (but carbide is better). Worst thread I ever tapped was an 1 1/8-12 in inconel. By hand, six holes, with a carbon tap because someone broke the good one (it may have been TiN coated - been a few years) trying to run it in the lathe at 60 rpm. It turned out fine and I got a great upper body workout.
For the size you're dealing with the taps are easy to break, so go slow. Turn it no more than a quarter (an eighth is better, at least until you get a feel for it), use a good tapping fluid like the ones named above.

[w5pv]

Tap majic,Rapid tap for stainless is the best but in a bind you can use any chornated fluid I have never used it but I suspect that brake cleaner fluid would work.Stainless needs a fluid that will evaporate pretty fast to keep it cool.

[plainsman456]

I have been reading old books about doing this type of thing and they mention using lard oil.

I assume that bacon grease would work.
And it is true that it work hardens rather fast when it warms up.

[fast ronnie]

Buttercut is a modified lard oil. I have never stuck a tap with it. Crisco also works well.
Like has been said above, use a good quality high speed steel tap, not carbon steel. The local hardware store taps usually don't get the job done as most are carbon steel.

[smokeywolf]

Crisco works exceedingly well on aluminum. Lard oil doesn't work too well on stainless, titanium or most other non-ferrous metals. Best I've found for drilling and tapping stainless is Rapid-Tap or something similar. There is one more that I have used extensively, called Molecular's Tapping Compound works quite well. But, that is found more often in the commercial market.

smokeywolf

[Silfield]

Good old fashioned spit works as a good tapping fluid for stainless as well!

[smokeywolf]

The volatile tapping fluids do a good job carrying heat away to reduce work hardening. One of the more troublesome problems when machining stainless.